In the past, natural scrapie and bovine spongiform encephalopathy (BSE) infections have essentiallynot been diagnosed in sheep homozygous for the A136R154R171 haplotype of the prion protein. Thisgenotype was therefore assumed to confer resistance to BSE and classic scrapie under naturalexposure conditions. Hence, to exclude prions from the human food chain, massive breeding effortshave been undertaken in the European Union to amplify this gene. We report the identification of 2natural scrapie cases in ARR/ARR sheep that have biochemical and transmission characteristicssimilar to cases of classic scrapie, although the abnormally folded prion protein (PrPSc) wasassociated with a lower proteinase-K resistance. PrPSc was clearly distinct from BSE prionspassaged in sheep and from atypical scrapie prions. These findings strongly support the idea thatscrapie prions are a mosaic of agents, which harbor different biologic properties, rather than aunique entity.

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Discussion

Epidemiologic and genetic data collected in recent decades have indicated that sheepcarrying the PrPC-encoding ARR haplotype only are resistant to natural TSE infections, whereasthose carrying the homozygous VRQ or ARQ haplotypes are changes highly susceptible. Thisassumption has been supported by genotyping data for several thousand sheep with scrapieworldwide: only 1 homozygous ARR carrier has been found. A case of classic scrapie inARR/ARR sheep in Japan was reported more than a decade ago (7). However, the validity of thisdiagnosis has been heavily challenged when it could not be reconfirmed independently, becauseno suitable frozen or formalin-fixed material was available. Our current report shows that classicscrapie cases can occur in homozygous ARR sheep and suggests that even the former report mayhave been an imperfect first demonstration of such a case.

The apparent resistance of sheep of the ARR/ARR genotype to both natural scrapie andexperimental BSE has triggered national authorities since the late 1990s (e.g., United Kingdom,the Netherlands, France), and since 2001 the EU, to implement a genetic selection and cullingpolicy in sheep to protect the human food chain from small ruminant TSEs and to eradicate TSEfrom affected flocks.

This global approach, even if valuable, considered scrapie as a single entity and did nottake into account any kind of TSE agent biodiversity. Sheep TSE agents have strikingly differentabilities to replicate in hosts expressing a spectrum of PrP variants. Sheep with genotypeARQ/ARQ in scrapie flocks are commonly affected by the disease (8). However, a historicalsheep scrapie brain pool (SSBP-1) transmits easily to VRQ homozygous or heterozygous sheepbut not to ARQ/ARQ animals (17). Similarly atypical scrapie cases (including the “Nor98” type)are more frequently found in AHQ and AF141RQ haplotype carriers than in sheep carryingexclusively other haplotypes. However, atypical cases have also been found in ARR/ARRanimals (18,19). Similarly, ability to of BSE to develop in ARR/ARR sheep was observed afterexperimental parenteral inoculation. However, in this case, higher transmission rates and shorterincubation periods were observed in sheep of the other genotypes, such as ARQ/ARQ, and

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AHQ/AHQ (20,21). The susceptibility of ARR/ARR sheep to an oral BSE challenge wasreported most recently (22).

Both BSE and atypical scrapie PrPSc have a characteristic molecular signature, whichallows rapid and reliable biochemical discrimination from each other and from classic scrapiePrPSc (3,23). In both cases of scrapie in ARR/ARR sheep in France and Germany, abnormalPrPSc harbored features (apparent molecular mass and glycotype) were very similar to thoseobserved in classic scrapie. However, at least in the S83 case, PrPSc seemed to have a remarkablylower PK resistance than that observed in a panel of scrapie isolates. This observation sustainsthe idea that the involved agent could belong to a particular scrapie agent group that cannot bedirectly identified by using the current biochemical criteria for TSE agent discrimination.The successful propagation of the S83 isolate in Tg338 mice that express the ovine VRQhaplotype and the persistence of its original biochemical signature (including the low PKresistance) allow the inference that this scrapie agent could also be present and could naturallypropagate in sheep that harbor genotypes other than ARR/ARR. The transmissibility andcontagiousness of the S83 isolate are currently under investigation in experimentally challengedsheep. These experiments should produce a better understanding of the susceptibility of eachgenotype to this agent and its capacity to spread efficiently in sheep flocks.The discovery of these 2 cases clearly indicates that the genetic resistance of ARR/ARRsheep to the so-called classic scrapie agent is not absolute. It also provides evidence that, ratherthan being a single entity, scrapie is a mosaic of infectious agents harboring different biologicproperties in its natural host. Finally, although many thousands of cases of classic scrapie havebeen reported in sheep of other PrP genotypes and hundreds of thousands of rapid tests havebeen performed in Europe since the implementation of active TSE surveillance in smallruminants began in 2001, the discovery of these 2 ARR/ARR cases supports the idea that suchinfections are extremely rare.

This work was supported by the German Ministry for Food, Agriculture and Consumer Protection, by theEuropean Union (EU) grant QLK-CT 2001-01309 (BSE in sheep), the EU-funded Network of Excellence“Neuroprion” (CT2004-506579), the French GIS prion strain typing group, and the EU program ACCESS (HPRTCT 2001-00131).

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Dr Groschup is head of the Institute for Novel and Emerging Infectious Diseases at the Friedrich-Loeffler-Institut, Insel Riems, Germany, and extraordinary professor at the Veterinary University of Hannover, Germany. Hisinterests focus on prion infections, including their diagnosis, transgenic detection, and molecular determinants ofinfectivity and transmission.

References

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http://www.cdc.gov/eid/content/13/8/pdfs/07-0077.pdf

Recently the question has again been brought up as to whetherscrapie is transmissible to man. This has followed reports that thedisease has been transmitted to primates. One particularly luridspeculation (Gajdusek 1977) conjectures that the agents of scrapie,kuru, Creutzfeldt-Jakob disease and transmissible encephalopathy ofmink are varieties of a single "virus". The U.S. Department ofAgriculture concluded that it could "no longer justify or permitscrapie-blood line and scrapie-exposed sheep and goats to be processedfor human or animal food at slaughter or rendering plants" (ARC 84/77)"The problem is emphasised by the finding that some strains of scrapieproduce lesions identical to the once which characterise the humandementias"

Whether true or not. the hypothesis that these agents might betransmissible to man raises two considerations. First, the safetyof laboratory personnel requires prompt attention. Second, actionsuch as the "scorched meat" policy of USDA makes the solution of theacrapie problem urgent if the sheep industry is not to suffergrievously.

Kuru and Creutzfeldt-Jakob disease of humans and scrapie disease of sheepand goats were transmitted to squirrel monkeys (Saimiri sciureus) that wereexposed to the infectious agents only by their nonforced consumption ofknown infectious tissues. The asymptomatic incubation period in the onemonkey exposed to the virus of kuru was 36 months; that in the two monkeysexposed to the virus of Creutzfeldt-Jakob disease was 23 and 27 months,respectively; and that in the two monkeys exposed to the virus of scrapiewas 25 and 32 months, respectively. Careful physical examination of thebuccal cavities of all of the monkeys failed to reveal signs or orallesions. One additional monkey similarly exposed to kuru has remainedasymptomatic during the 39 months that it has been under observation.

This is provided by the statistically significant increase in the incidenceof sheep scrape from 1985, as determined from analyses of the submissionsmade to VI Centres, and from individual case and flock incident studies.........

http://www.bseinquiry.gov.uk/files/yb/1994/02/07002001.pdf

AS implied in the Inset 25 we must not _ASSUME_ thattransmission of BSE to other species will invariablypresent pathology typical of a scrapie-like disease.

Edited by Stanley B. Prusiner, University of California, San Francisco, CA,and approved September 12, 2005 (received for review March 21, 2005)

Scrapie in small ruminants belongs to transmissible spongiformencephalopathies (TSEs), or prion diseases, a family of fatalneurodegenerative disorders that affect humans and animals and can transmitwithin and between species by ingestion or inoculation. Conversion of thehost-encoded prion protein (PrP), normal cellular PrP (PrPc), into amisfolded form, abnormal PrP (PrPSc), plays a key role in TSE transmissionand pathogenesis. The intensified surveillance of scrapie in the EuropeanUnion, together with the improvement of PrPSc detection techniques, has ledto the discovery of a growing number of so-called atypical scrapie cases.These include clinical Nor98 cases first identified in Norwegian sheep onthe basis of unusual pathological and PrPSc molecular features and "cases"that produced discordant responses in the rapid tests currently applied tothe large-scale random screening of slaughtered or fallen animals.Worryingly, a substantial proportion of such cases involved sheep with PrPgenotypes known until now to confer natural resistance to conventionalscrapie. Here we report that both Nor98 and discordant cases, includingthree sheep homozygous for the resistant PrPARR allele (A136R154R171),efficiently transmitted the disease to transgenic mice expressing ovine PrP,and that they shared unique biological and biochemical features uponpropagation in mice. These observations support the view that a trulyinfectious TSE agent, unrecognized until recently, infects sheep and goatflocks and may have important implications in terms of scrapie control andpublic health.

Dormont*, and Jean-Philippe Deslys* et al, that The agent responsiblefor French iatrogenic growth hormone-linked CJD taken as a control isvery different from vCJD but is similar to that found in one case ofsporadic CJD and one sheep scrapie isolate;